Chiral nematic polycarbonates

ABSTRACT

A chiral nematic polycarbonate having carbonate units, of the formula I 
     where the w/x/y/z molar ratio is 1 to 20/1 to 5/0 to 10/0 to 10, 
     A is a mesogenic group of the formula ##STR1## or ##STR2## ; and B is a chiral group.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to liquid crystalline chiral nematicpolycarbonates.

2. Description of the Background

Heating of shape-anisotropic substances may result in liquid crystallinephases, called mesophases. The individual phases differ by the spatialarrangement of the molecular centers on the one hand and by themolecular arrangement with respect to the long axes on the other hand(G. W. Gray, P. A. Winsor, Liquid Crystals and Plastic Crystals, EllisHorwood Limited, Chichester 1974). The nematic liquid crystalline phaseis distinguished by parallel orientation of the long axes of themolecule (one-dimensional order state). Provided that the moleculesforming the nematic phase are chiral, what results is a chiral nematic(cholesteric) phase in which the long axes of the molecules form ahelical superstructure perpendicular thereto (H. Baessler,Festkorperprobleme XI, 1971). The chiral moiety may either be present inthe liquid crystalline molecule itself or be added as doping substanceto the nematic phase, in which case the chiral nematic phase is induced.This phenomenon was investigated first on cholesterol derivatives (forexample H. Baessler, M. M. Labes, J. Chem. Phys. 52 (1970) 631)).

The chiral nematic phase has special optical properties: a high opticalrotation and a pronounced circular dichroism which arises owing toselective reflection of circularly polarized light within the chiralnematic layer. The different colors which are apparent depending on theangle of view depend on the pitch of the helical superstructure which inturn depends on the twisting ability of the chiral component. It ismoreover possible to alter the pitch, and thus the wavelength range ofthe selectively reflected light, of a chiral nematic layer in particularby changing the concentration of a chiral doping substance. Chiralnematic systems of this type have interesting possibilities forpractical application. Thus, it is possible by incorporating chiralmoieties into mesogenic acrylic esters and orienting in the chiralnematic phase, eg. after photopolymerization, to prepare a stablecolored network, although it is not then possible to change itsconcentration of chiral component (G. Galli, M. Laus, A. Angelon,Makromol. Chemie 187 (1986) 2289). It is possible by admixingnoncrosslinkable chiral compounds with nematic acrylic esters and byphotopolymerization to prepare a colored polymer which still containslarge amounts of soluble components (I. Heyndricks, D. J. Broer, Mol.Cryst. Liq. Cryst. 203 (1991) 113). It is furthermore possible by randomhydrosilylation of mixtures of cholesterol derivatives andacrylate-containing mesogens with defined cyclic siloxanes andsubsequent photopolymerization to obtain a chiral nematic network inwhich the chiral component may comprise up to 50% of the materialemployed; however, these polymers still contain marked amounts ofsoluble materials (F. H. Kreuzer, R. Mauerer, Ch. Muller-Rees, J.Stohrer, Presentation No. 7, 22nd meeting on liquid crystals, Freiburg,1993).

DE-A-35 35 547 describes a process in which a mixture ofcholesterol-containing monoacrylates can be converted byphotopolymerization into chiral nematic layers. However, the totalcontent of the chiral component in the mixture is about 94%. Althoughthe mechanical stability of such a material as pure side-chain polymeris not very great, the stability can be increased only by highlycrosslinking diluents.

Numerous chiral nematic polyesters in which the mesogenic structures areincorporated into the main chain are also generally known, eg. from S.Vilasagar, A. Blumstein, Mol. Cryst. Liq. Cryst. (1980), 56 (8), 263-9;A. Blumstein, S. Vilasagar, S. Ponratham, S. B. Clough, R. B. Blumstein,G. Maret, J. Polym. Sci., Polym. Phys. Ed. (1982), 20 (5), 877-92; E.Chiellini, G. Galli, C. Malanga, N. Spassky, Polym. Bull. (1983), 9(6-7), 336-43; H. J. Park, J. I. Jin, R. W. Leng, Polymer (1985), 26(9), 1301-6; J. I. Jin, E. J. Choi, K. Y. Lee, Polym. J. (1986), 18 (1),99.101; J. I. Jin, S. C. Lee, S. D. Chi, J. H. Chang; Pollimo (1986), 10(4), 382-8; J. I. Jin, E. J. Choi, B. W. Jo, Pollimo (1986), 10 (6),635-40; J. M. G. Cowie, E. H. Wu, Makromol. Chem. (1988), 189 (7),1511-16; V. V. Zuev, I. G. Denisov, S. S. Skorokhodov, Vysokomol.Soedin., Ser. A (1989, 31 (5), 1056-61; A. S. Angeloni, D. Caretti, C.Carlini, E. Chiellini, G. Galli, A. Altomare, R. Solaro, M. Laus, Liq.Cryst. (1986), 4 (5), 513-27; K. Fujishiro, R. W. Lenz, Macromolecules(1992), 25 (1), 88-95; K. Fujishiro, R. W. Lenz, Macromolecules (1992),25 (1), 81-7; V. V. Zuev, I. G. Denisov, S. S. Skorokhodov, Vysokomol.Soedin., Ser. B (1992), 34 (3), 47-54; V. V. Zuev, I. G. Denisov, S. S.Skorokhodov Vysokomol. Soedin., Ser. B (1989), 31 (2), 130-2.

These polyesters usually show narrow ranges of existence of the chiralnematic phase and contain predominantly open-chain chiral componentswhich have little twisting ability so that relatively large contents ofthese components are necessary in order to obtain a color. This meansthat the choice of the remaining polyester constituents is restricted,for example with respect to their mechanical properties.

DE-A-19504913.6 describes chiral nematic polyesters with chiral diolcomponents which have a strong twisting effect, in particulardianhydride saccharides, and with wide liquid crystalline phase ranges.

EP-A-682 092 describes surface coatings based on chiral nematicpolymers. The examples mentioned are exclusively polyesters prepared bypolycondensation of dicarboxylic acids and diols. Polycarbonates are notmentioned.

Chiral nematic polycarbonates have not hitherto been disclosed. Thecarbonate group is, because of its nonlinear structure, less suitablethan the ester group for stabilizing a liquid crystalline phase.Nevertheless, it has been possible to prepare aromatic polycarbonateswhich contain para-linked diphenols, in particular4,4'-dihydroxybiphenyl (DHB), and are able to form a nematic phase overa wide temperature range (Kricheldorf, H. R.; Lubbers, D., Makromol.Rapid Communc. 1989, 10, 383; Kricheldorf, H. R.; Lubbers, D.,Macromolecules 1990, 23, 2656; Sun, S.-J.; Chang, TzCh., J. Polym. Sci.,Part A, Polym. Chem. 1993, 31, 2237). However, there are problems inusing chiral comonomers because they destabilize the liquid crystallinephase of polycarbonates more strongly than do their nonchiral analogs.

SUMMARY OF THE INVENTION

The invention relates to chiral nematic polycarbonates having carbonateunits which comprise a mesogenic group, and carbonate units whichcomprise a chiral group, and to chiral nematic polycarbonates whichadditionally comprise carbonate units having a photoreactive groupand/or carbonate units having another, nonchiral group which is, inparticular, a mesogenic and/or solubility-improving group. Said unitsare groups which can be derived from diols by removing the two hydroxylgroups. They are therefore also referred to as diol units hereinafter.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The chiral nematic polycarbonates according to the invention preferablycorrespond to formula I ##STR3## where the w/X/y/z molar ratio is about1 to 20 / about 1 to 5 / about 0 to 10 / about 0 to 10. A w/x/y/z molarratio of about 1 to 5 / about 1 to 2 / about 0 to 5 / about 0 to 5 isparticularly preferred.

In formula I,

A is a mesogenic group of the formula ##STR4## or ##STR5## B is a chiralgroup of the formula ##STR6## D is a photoreactive group of the formula##STR7## or ##STR8## and E is another, nonchiral group of the formula##STR9## where, in the above formulae, L is alkyl, alkoxy, halogen,COOR, OCOR, CONHR or NHCOR,

X is S, O, N, CH₂ or a single bond,

R is alkyl or hydrogen,

A is a single bond, (CH₂)_(n), O(CH₂)_(n), S(CH₂)_(n), NR(CH₂)_(n),##STR10## or ##STR11## R¹ is hydrogen, halogen, alkyl or phenyl, and nis an integer from 1 to 15.

When R¹ is alkyl, halogen and A is a single bond, or when R¹ is H oralkyl and A is ##STR12## the groups improve the solubility. Examplesthereof are ##STR13##

Isosorbide, isomannide and/or isoidide is the preferred chiralcomponent.

Saccharide derivatives based on dianhydrosorbide and the stereoisomersthereof are distinguished by a very great twisting ability. It ispossible by suitable choice of the ratio between the chiral diol and anonchiral diol, preferably phenylhydroquinone, to stabilize the liquidcrystalline phase ranges to above 450° C.

The content of chiral diol structural units is preferably in the rangefrom 1 to 80 mol % of the total content of diol structural units,particularly preferably 2 to 20 mol %, depending on the interference huerequired.

The following abbreviations apply for the purpose of the presentapplication:

4,4'-dihydroxybiphenyl: DHB; methylhydroquinone: MHQ;

4,4'-dihydroxychalcone: DHC; hydroquinone 4-hydroxybenzoate: HQHB;2,5-bis(4-hydroxybenzylidene)cyclopentanone: BHBC.

Alkyl (also in alkoxy etc.) is preferably C₁ -C₆ -alkyl, in particularC₁ -C₄ -alkyl, such as methyl, ethyl, n-propyl, isopropyl, n-butyl,isobutyl, sec-butyl, tert-butyl, n-pentyl and n-hexyl.

Hal is F, Cl, Br and I.

The polycarbonates according to the invention can be prepared by varioustypes of polycondensation of diols with phosgene or diphosgene. Examplesof diols which can be employed are the terminally hydroxylated groups A,B, D and E in formula I. They are employed in the A/B/D/E molar ratio ≈1to 20/1 to 5/0 to 10/0 to 10, particularly preferably in the A/B/D/Emolar ratio ≈1 to 5/1 to 2/0 to 5/0 to 5. Examples of conventional typesof polycondensation are interfacial polycondensation, meltpolycondensation and solution polycondensation.

In interfacial polycondensation, the diols forming the mesogenic group,the chiral group and, where appropriate, the photoreactive and thesolubility-improving group are dissolved together with phosgene or,preferably, the considerably less hazardous diphosgene (Cl--COCCl₃) ortriphosgene and a catalytic amount of an amine, for exampletriethylamine or a quaternary ammonium salt such astriethylbenzylammonium chloride, in a suitable organic solvent, eg. anether such as tetrahydrofuran or dioxane, a chlorinated hydrocarbon suchas dichloromethane or chlorobenzene. An aqueous base, eg. sodiumhydroxide solution, is added to this solution, and the two phases aremixed together, eg. by vigorous stirring. The stirring is preferablyaccompanied by cooling. If the polymer is soluble in the solvent used,the organic phase is separated off and the polycarbonate is isolatedtherefrom in a conventional way, eg. by taking up in methanol andfiltering off. If, on the other hand, the polymer precipitates from thesolvent or a gel is formed, the reaction mixture is diluted ifnecessary, eg. with methanol, and the polymer is filtered off. It isalso possible to employ as alternatives to phosgene or diphosgene thechlorinated carbonic diesters of the diols to be condensed.

In melt polycondensation, the dicarbonate of one of the diols formingthe mesogenic group, the chiral group and, where appropriate, thesolubility-improving or the photoreactive group is reacted with thediols forming the remaining groups. The reaction is carried out atelevated temperature, generally in the range from 120° C. to 300° C., italso being possible for the temperature to be increased stepwise in thisrange. The resulting polymer is dissolved or suspended in one of theabovementioned suitable solvents and, where appropriate, precipitatedwith methanol.

In solution polycondensation, the diols forming the mesogenic group, thechiral group and, where appropriate, the other nonchiral group and thephotoreactive group are dissolved in an amine, preferably a tertiary oraromatic amine, for example pyridine. Diphosgene dissolved in one of theabovementioned suitable solvents is added to this solution. The reactionis generally carried out at from about 0° C. to ambient temperature, butthe temperature can also be higher, in particular in order to completethe reaction. The mixture is then worked up in a conventional way. Thechlorinated carbonic diesters of the diols to be polymerized can also beused, as alternative to the use of diphosgene, in the solutionpolycondensation.

Of the condensation methods mentioned, interfacial polycondensation andsolution polycondensation are preferred, the latter especially when morehydrophilic monomers, such as isosorbide, are employed, these beingtransferred from the aqueous into the organic phase considerably lesswell than the other monomers with which they are to be condensed in theinterfacial polycondensation.

If the polycarbonate is required to have a low viscosity, a chainterminator, eg. cinnamoyl chloride, can be added to the reactionmixture.

The polycarbonates according to the invention have an inherent viscosityη_(inh) of about 0.08 to 3 dl/g, in particular about 0.1 to 2 dl/g,measured at 20° C. with c=2 g/l in dichloromethane/trifluoroacetic acid(ratio 4/1 by volume).

The glass transition temperature (determined by DSC) of thepolycarbonates according to the invention is generally in the range fromabout 50 to 300° C., in particular about 60 to 200° C. The melting pointof the polymers according to the invention is generally in the rangefrom about 75 to 450° C., in particular about 90 to 350° C.

The polycarbonates according to the invention contain randomlydistributed units.

The polycarbonates according to the invention are able to form what iscalled a Grandjean texture, which confirms the cholesteric effect of thechiral groups used.

The polymers according to the invention are particularly suitable assurface-coating materials, as optical components and as chiral nematiccoloring materials. They can be used as coloring surface-coating system(eg. as automobile paint or effect sheets), or else for producingcolored pigments. The coloring structure of the polymer can be fixed byrapid cooling or photochemical crosslinking of the chiral nematic phase.Colored pigments can be produced, for example, by detaching the orientedpolymer film from the coated surface and milling to pigments in the formof small plates. In contrast to the process described in DE-A 42 40 743,in this case crosslinking of the polymer is not absolutely necessary.The polymer can be used as surface-coating system in the form of apowder, a melt or a solution (eg. in N-methylpyrrolidone ordimethylformamide). In the simplest case, the orientation of the systemtakes place by heat treatment of the coated surface and can be improved,where appropriate, by the action of mechanical, electrical or magneticforces.

The following Examples illustrate the invention without restricting it,however:

The physical properties of the polymers described in the examples areindicated in Table 1.

EXAMPLE 1 Chiral Nematic Polycarbonate with(S)-(2-methylbutylthio)hydroquinone as Diol Forming the Chiral Group

DHB (15 mmol), MHQ (7.5 mmol), (S)--(2-Methylbutylthio)hydroquinone (7.5mmol), diphosgene (16.5 mmol) and 1 drop of triethylamine were dissolvedin 100 ml of dry cold dichloromethane. 80 ml of 1N sodium hydroxidesolution were added to this solution, and the two phases were stirredwith an Ultra Turrax homogenizer for 10 min and then with a normalmechanical stirrer for 20 min while cooling in ice. The organic phasewas then separated off in a separating funnel, added to 800 ml ofmethanol and filtered. The isolated polymer was dissolved indichloromethane and reprecipitated in methanol. Finally, thepolycarbonate was dried at 80° C. under reduced pressure. The yield fromthis interfacial polycondensation was 88%. The resulting polymer 1 isdescribed by the following formula: ##STR14## with the x/y/z molarratio=5/1/4.

EXAMPLE 2 Chiral Nematic Polycarbonate with Isosorbide as Diol Formingthe Chiral Group

A solution of diphosgene (16.5 mmol) in 20 ml of dichloromethane wasadded dropwise to a solution of DHB (15 mmol), MHQ (7.5 mmol) andisosorbide (7.5 mmol) in 30 ml of pyridine. The mixture was left toreact at about 5 to 10° C. for 30 min and then at room temperature forabout one hour. The mixture was then added to methanol and filtered. Theisolated polymer was dissolved in dichloromethane and reprecipitated inmethanol. The resulting polycarbonate of the formula 2 with the x/y/zmolar ratio=21/1 (2a) was dried at 80° C. under reduced pressure. Asecond polycarbonate of the formula 2 with the x/y/z molar ratio=4/1/3(2b) was prepared in the same way but with 3.75 mmol of MHQ and 11.25mmol of isosorbide. ##STR15##

The yield was 98% in both cases.

EXAMPLE 3 Chiral Nematic Polycarbonates with DHC as Photoreactive Group

A solution of diphosgene (16.5 mmol) in dichloromethane (20 ml) wasadded dropwise to a solution of DHB (15 mmol), DHC (7.5 mmol) andisosorbide (7.5 mmol) in pyridine (30 ml). The reaction mixture wasstirred at about 5 to 10° C. while cooling in ice for 30 min andsubsequently at about 20 to 25° C. for about 1 h. The reaction mixturewas then added to cold methanol, and the precipitated polycarbonate ofthe formula 3 ##STR16## with the x/y/z ratio of molar amounts=2/1/1 (3a)was filtered off, washed with methanol and dried at about 80° C. underreduced pressure. Three other polycarbonates with x/y/z molarratios=3/2/1 (3b), =4/3/1 (3c) and =5/4/1 (3d) were prepared in asimilar way. The amounts of DHC and isosorbide used for 3b were 10 mmoland 5 mmol, for 3c were 11.25 mmol and 3.75 mmol and for 3d were 12 moland 3 mmol, respectively. The yield was 98% for each of 3a-c, and was97% for 3d. UV radiation of thin films of the polycarbonates 3a to 3dwith UV from a mercury vapor lamp for 5 minutes rendered the polymersinsoluble in dichloromethane. DHC is thus also suitable as crosslinkerunit in chiral nematic polycarbonates.

EXAMPLE 4 Chiral Nematic Polycarbonates with HQHB as Diol Forming theMesogenic Group

A solution of diphosgene (16.5 mmol) in 20 ml of dichloromethane wasadded dropwise to a solution of HQHB (15 mmol), DHC (7.5 mmol) andisosorbide (7.5 mmol) in 30 ml of pyridine. The mixture was left toreact at about 5 to 10° C. for about 30 min and then at room temperaturefor about one hour. The mixture was then taken up in methanol, and theprecipitated polycarbonate of the formula 4 ##STR17## with the x/y/zmolar ratio=2/1/1 (4a) was filtered off and dried at about 80° C. underreduced pressure. Three other polycarbonates with x/y/z molarratios=3/2/1 (4b), =4/3/1 (4c) and =5/4/1 (4d) were prepared in asimilar way. The amounts of DHC and isosorbide used for 4b were 10 mmoland 5 mmol, for 4c were 11.25 mmol and 3.75 mmol and for 4d were 12 mmoland 3 mmol, respectively. The yields were 94% for polycarbonate 4a, 93%for 4b and 96% for each of 4c and 4d.

EXAMPLE 5 Chiral Nematic Polycarbonates with BHBC as Crosslinker Unit

A solution of diphosgene (16.5 mmol) in 20 ml of dichloromethane wasadded dropwise to a solution of HQHB (10 mmol), BHBC (10 mmol) andisosorbide (10 mmol) in 30 ml of pyridine. The mixture was left to reactat about 5 to 10° C. for about 30 min and then at room temperature forabout one hour. The mixture was then added to methanol and filtered. Theresulting polymer of the formula 5 ##STR18## with the x/y/z molarratios=1/1/1 (5a) was dissolved in dichloromethane and reprecipitated inmethanol. Finally, the polycarbonate was dried at about 80° C. underreduced pressure. Three other polycarbonates of the formula 5 wereprepared in the same way. The x/y/z molar ratios were 2/1/1 for 5b,3/2/1 for 5c and 4/3/1 for 5d. The amounts of HQHB, BHBC and isosorbideemployed were 15 mmol, 7.5 mmol and 7.5 mmol for 5b, 15 mmol, 10 mmoland 5 mmol for 5c and 15 mmol, 11.25 mmol and 3.75 mmol for 5d. Theyield was 84% for 5a, 91% for 5b, 79% for 5c and 90% for 5d.

Table 1 indicates the physical properties (inherent viscosity (η_(inh)),optical rotation ([α]_(D)), glass transition temperature (T_(g)) andclearing point (T_(i))), the observed textures of the liquid crystallinephases and the interference colors of polymers 1 to 5.

                  TABLE 1                                                         ______________________________________                                        Poly-                                                                           and                                                                           oligo- η.sub.inh.sup.1) [α].sub.D.sup.2) Tg.sup.3) Ti.sup.4)                                              mer (dl/g) [degrees] (°                                               C.) (° C.) Texture Color        ______________________________________                                        1    1.48   -1.2     115  >300   Grand-                                                                              bluish                                        jean                                                                     2a 0.68 +43 121 >340.sup.z) Grand- bluish                                          jean                                                                     2b 0.86 +28                                                                  (?) >360.sup.z) Grand- bluish                                                       jean                                                                     3a 0.50 +41.6 116 >340.sup.z) Grand- bluish                                        jean                                                                     3b 0.38 +33.0 118 >340.sup.z) Grand- bluish                                        jean                                                                     3c 0.40 +21.1 116 >350.sup.z) Grand- bluish                                        jean                                                                     3d 0.33 +19.6 111 >350.sup.z) Grand- bluish                                        jean                                                                     4a 0.27 +38.7* 104 290-325 Grand- blue in reflected                                jean light, yellowish-                                                         orange in trans-                                                              mitted light                                                            4b 0.50 +30.3* 102 280-300 Grand- blue                                             jean                                                                     4c 0.62 +23.5* 101 310-330 Grand- blue                                             jean                                                                     4d 0.66 +17.1* 101 325->350 Grand- blue                                            jean                                                                     5a 0.58  146 >310.sup.z)v) Grand- bluish                                           jean                                                                     5b 0.47  126 >315.sup.z)v) Grand- bluish                                           jean                                                                     5c 0.45  146 >330.sup.z)v) Grand- bluish                                           jean                                                                     5d 0.88  135 >320.sup.z)v) Grand- bluish                                           jean                                                                   ______________________________________                                         .sup.1) measured at 20° C., c = 2 g/l in                               dichloromethane/trifluoroacetic acid (4/1)                                    .sup.2) measured at 25° C., c = 5 g/l or *2 g/l in                     dichloromethane/trifluoroacetic acid (4/1)                                    .sup.3) DSC measurement, heating rate 20° C./min                       .sup.4) Polarizing microscope, heating rate 10° C./min or .sup.#       optical microscope, heating rate 20° C./min                            .sup.z) thermal decomposition                                                 .sup.v) thermal crosslinking                                             

We claim:
 1. A chiral nematic polycarbonate having carbonate units, ofthe formula I ##STR19## where the w/x/y/z molar ratio is 1 to 20/1 to5/0 to 10/0 to 10, A is a mesogenic group of the formula ##STR20## B isa chiral group of the formula ##STR21## D is a photoreactive group ofthe formula ##STR22## and E is another, nonchiral group of the formula##STR23## where, in the above formulae L is alkyl, alkoxy, halogen,COOR, OCOR, CONHR or NHCOR,X is S, O, N, CH₂ or a single bond, R isalkyl or hydrogen, A¹ is a single bond, (CH₂)_(n), O(CH₂)_(n),S(CH₂)_(n), NR(CH₂)_(n), ##STR24## or ##STR25## R¹ is hydrogen, halogen,alkyl or phenyl, and n is an integer from 1 to
 15. 2. The chiral nematicpolycarbonate as claimed in claim 1, which has an inherent viscosity ofabout 0.08 to 3 dl/g, measured in dichloromethane/trifluoroacetic acid(4:1, v/v) at 20° C. and at a concentration of 2 g/l.
 3. The chiralnematic polycarbonate of claim 1, which has a glass transitiontemperature in the range from about 50 to 300° C.
 4. A pigmentcomprising a chiral nematic polycarbonate of claim
 1. 5. A coatingcomposition comprising at least one chiral nematic polycarbonate ofclaim
 1. 6. The process as claimed in claim 1, wherein cinnamoylchloride is added as chain terminator.
 7. A process for preparing chiralneumatic polycarbonates, which comprises condensing compounds containingthe mesogenic groups and chiral groups of claim 1, and, optionally,photoreactive groups or solubility-improving groups or thermallycrosslinking groups or a combination thereof, each in the form of acorresponding diol compounds, with phosgene or diphosgene.
 8. The chiralnematic polycarbonate as claimed in claim 1, which has an inherentviscosity η_(inh) of about 0.08 to 3 dl/g measured at 20° C. with c=2g/l in dichloromethane/trifluoroacetic acid (ratio 4/1 by volume). 9.The chiral nematic polycarbonate as claimed in claim 8, having aninherent viscosity of 0.1 to 2 dl/g.
 10. The chiral nematicpolycarbonate as claimed in claim 1, which has a glass transitiontemperature of from about 50° C. to 300° C.
 11. The chiral nematicpolycarbonate as claimed in claim 1, which has a melting point of fromabout 75° C. to 450° C.